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Commit 1f364c8c authored by Marc Zyngier's avatar Marc Zyngier
Browse files

arm64: VHE: Add support for running Linux in EL2 mode 



With ARMv8.1 VHE, the architecture is able to (almost) transparently
run the kernel at EL2, despite being written for EL1.

This patch takes care of the "almost" part, mostly preventing the kernel
from dropping from EL2 to EL1, and setting up the HYP configuration.

Reviewed-by: default avatarChristoffer Dall <christoffer.dall@linaro.org>
Acked-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
parent ae7e27fe

arch/arm64/Kconfig

+13 −0
Original line number Diff line number Diff line
@@ -750,6 +750,19 @@ config ARM64_LSE_ATOMICS 
	  not support these instructions and requires the kernel to be

	  built with binutils >= 2.25.



config ARM64_VHE

	bool "Enable support for Virtualization Host Extensions (VHE)"

	default y

	help

	  Virtualization Host Extensions (VHE) allow the kernel to run

	  directly at EL2 (instead of EL1) on processors that support

	  it. This leads to better performance for KVM, as they reduce

	  the cost of the world switch.



	  Selecting this option allows the VHE feature to be detected

	  at runtime, and does not affect processors that do not

	  implement this feature.



endmenu



endmenu

arch/arm64/kernel/head.S

+27 −1
Original line number Diff line number Diff line
@@ -30,6 +30,7 @@ 
#include <asm/cache.h>

#include <asm/cputype.h>

#include <asm/kernel-pgtable.h>

#include <asm/kvm_arm.h>

#include <asm/memory.h>

#include <asm/pgtable-hwdef.h>

#include <asm/pgtable.h>
@@ -464,9 +465,27 @@ CPU_LE( bic x0, x0, #(3 << 24) ) // Clear the EE and E0E bits for EL1 
	isb

	ret



2:

#ifdef CONFIG_ARM64_VHE

	/*

	 * Check for VHE being present. For the rest of the EL2 setup,

	 * x2 being non-zero indicates that we do have VHE, and that the

	 * kernel is intended to run at EL2.

	 */

	mrs	x2, id_aa64mmfr1_el1

	ubfx	x2, x2, #8, #4

#else

	mov	x2, xzr

#endif



	/* Hyp configuration. */

2:	mov	x0, #(1 << 31)			// 64-bit EL1

	mov	x0, #HCR_RW			// 64-bit EL1

	cbz	x2, set_hcr

	orr	x0, x0, #HCR_TGE		// Enable Host Extensions

	orr	x0, x0, #HCR_E2H

set_hcr:

	msr	hcr_el2, x0

	isb



	/* Generic timers. */

	mrs	x0, cnthctl_el2
@@ -526,6 +545,13 @@ CPU_LE( movk x0, #0x30d0, lsl #16 ) // Clear EE and E0E on LE systems 
	/* Stage-2 translation */

	msr	vttbr_el2, xzr



	cbz	x2, install_el2_stub



	mov	w20, #BOOT_CPU_MODE_EL2		// This CPU booted in EL2

	isb

	ret



install_el2_stub:

	/* Hypervisor stub */

	adrp	x0, __hyp_stub_vectors

	add	x0, x0, #:lo12:__hyp_stub_vectors